Conducting polymers (CPs) have been applied in a number of fields ranging from flexible electronics and sensing to energy storage. The growing interest in these materials stems from their unique and tunable physical and chemical properties. CPs have conjugated double-bonded backbone that provides electrical conductivity after doping. Electrochemical oxidation and reduction of these polymers can change their color, volume, conductivity, and wettability. Moreover, CPs can easily be decorated with functional molecules including bioactive proteins and drugs or can entrap these molecules for controlled release upon electrical stimulation. In the biomedical field, surfaces with patterned films of CP offer attractive platforms for studies of in vitro cell attachment and growth, tissue regeneration, neural electrodes, or biosensing. In this context, polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) have become particularly popular due to their superior conductivity, chemical stability, and biocompatibility.
PPy and PEDOT polymers are commonly synthesized through chemical or electrochemical polymerization. In addition, CPs can be patterned either through selective removal of parts of an existing film or selective deposition of the polymer. To date, both approaches have been employed through variety of techniques such as inkjet printing, infrared laser, photolithography, e-beam lithography, dip-pen nanolithography, and microcontact printing. Among these techniques, microcontact printing offers a low-cost and versatile approach to pattern CP films, with resolutions acceptable for most biomedical applications, compared to other methods where sophisticated instruments are often required.
Microcontact printing is accessible to any ordinary laboratory since stamps are prepared from elastomeric materials, such as polydimethylsiloxane (PDMS), casted from a microfabricated mold. Within the past few years, hydrogels have been explored as an alternative for the traditional PDMS stamps in microcontact printing of hydrophilic substances. The porous and hydrated nature of hydrogels enables these stamps to absorb aqueous solutions of cells and biomolecules for subsequent patterning. These stamps have also been utilized in fabrication of micro and nano-scale structures on glass substrates.
Larsen and colleagues employed hydrogel stamps to deliver an etchant chemical for selective removal of parts of a preformed CP film, producing a patterned polymer film. T. S. Hansen, K. West, O. Hassager, N. B. Larsen, Adv. Mater. 2007, 19, 3261. In another study, these authors further extended the application of hydrogel stamps to generate patterned CP films with various chemistries in register. This subtractive approach, however, required several consecutive steps for generating the patterned CP film with multiple chemistries. Lind, et al., Langmuir 2012, 28, 6502. Accordingly a continuing need exists for preparing conductive polymers and preparing patterned conductive polymers.